Radio antenna



Dec. 2, 1958 c. E. BERLIN 2,863,147

RADIO ANTENNA N Filed May 1'7, 1955- 2 Sheets-Sheet 1 INVENTOR.

(i/4,915.5 5. BfRA/A/ B Y gun M 396% United States This invention relates to a radio antenna and particularly to a radio antenna for use with vehicles such as automobiles.

A satisfactory radio antenna for moving vehicles such as automobiles must fulfill certain basic requirements. Such an antenna must be omnidirectional, that is, it must be responsive to radio frequency signals from all directions. In addition, such an antenna must have good sensitivity over the entire range of radio frequencies. A further requirement of such an antenna is that it be capable of discriminating against ignition interference. It is also desirable that the antenna resonant at some intermediate frequency between the ends of the broadcast band and also have a fiat curve of sensitivity at all frequencies. In the present-day automobile radios, the radios are provided with a trimmer capable of compensating for capacitance of the antenna and lead up to 85 micro microfarads. It is therefore a further requirement of a satisfactory antenna for automobiles that the capacitance of the antenna and the lead to theradio be less than 85 micro microfarads.

A further requirement of a satisfactory antenna for automobiles is that the factor Q be high. The factor Q is obtained by testing circuits and has generally been accepted as a measure of the performance of an antenna. The factor Q is designated as the ratio of reactance to resistance of a coil.

At the present time radio antennas for automobiles generally comprise a slender wire or tube which projects upwardly from the automobile and are commonly known as whip antennas. Such antennas are subject to bending or breakage when contacting a structure such as a garage or passing through an area where there are low branches of trees. In addition, many of the whip antennas are constructed for variable length and require manual operation or expensive automatic means for elevating and lowering the antenna.

lt is therefore an object of this invention to provide an antenna for automobiles which is small in size and may be located beneath the automobile.

It is a further object of this invention to provide such an antenna which is omnidirectional and has high sensitivity.

It is a further object of this invention to provide such an antenna which effectively overcomes ignition interference.

Another object of the invention is to provide such an antenna which has a capacitance of less than 85 micromicrofarads.

Another object of the invention is to provide such an antenna which resonates at an intermediate frequecny and has a reasonably fiat sensitivity curve over a broadcast band.

Another object of the invention is to provide such an antenna which has a high factor Q.

Basically, the antenna of this invention comprises a hollow, generally annular casing in which is positioned atent a toroid coil of helically wound ribbon having the ends thereof spaced from each other. A bar of ferrite is positioned within one end of the helically wound ribbon. In addition, a pair of random wound coils are contained within the casing, the coils being of unequal impedance and connected in series with the toroid coil of helically wound ribbon. A tap is connected to the toroid coil near the end thereof opposite the end in which the ferrite piece is positioned and projects through the casing. This tap comprises a static wire which projects outwardly into the area surrounding the casing. A second tap is connected between the pair of random wound coils and projects through the casing and in turn is connected to the car radio by a lead. The toroid coil of helically wound ribbon and pair of random wound coils are electrically insulated from the casing by a suitable coating such as a wax-dipped coating. The exterior of the casing is protected from the effect of moisture, stones, gravel and road-treating chemicals by a suitable coating on the outer surfaces. The entire antenna is mounted by suitable means beneath the auto-mobile which preferably includes means permitting limited movement of the antenna relative to the automobile to prevent damage to the antenna, in the event the antenna strikes an obstruction.

In the drawings:

Fig. l is an elevational view of an antenna embodying the invention showing the manner in which it may be mounted beneath an automobile.

Fig. 2 is a part sectional plan view of the antenna with part of the casing removed.

Fig. 3 is a sectional elevational view taken along the line 3-3 of Fig. 2.

Fig. 4 is a fragmentary sectional view taken along the line 44 on Fig. 2.

Fig. 5 is a fragmentary sectional view taken along the line 5-5 on Fig. 2.

Fig. 6 is an end elevational view of the antenna mounted in position beneath an automobile.

Fig. 7 is a schematic wiring diagram of the electrical circuit utilized in the antenna.

Fig. 8 is a sectional view of a modified form of the antenna.

Referring to Fig. 1, an antenna 10 is positioned beneath automobile frame 11 by suitable mounting means 12 and is connected to the car radio by a lead cable 13. As shown in Figs. 2 and 3, the antenna 10 includes housing or casing 14 composed of two D-shaped metal halves 15 and 16 having a generally U-shaped cross section and joined together at their abutting edges as at 17 and 18 by bending down and clinching. The two halves thus form a generally annular, D-shaped hollow case. Within the case are positioned a toroid coil 19 of helically wound metal ribbon and a random wound coil 2d of coated wire.

As shown in Figs. 4 and 5, the metal ribbon which forms the toroid coil 19 is helically wound on a core of plastic or cardboard material 19' with the windings spaced apart equally. One end of the metal ribbon is wound around a straight ferrite piece 21 and connected to the toroid coil 19 to form a D-shaped winding.

The randon wound coil 20 comprises a multiplicity of wires random wound in a generally D-shaped form and positioned beneath the toroid coil 19. A tap 22 is formed in the random Wound coil by looping the wire at a point intermediate the length of the coil, thus dividing the random wound coil into a pair of coils connected in series. The ends of the random wound coil 20 are connected to the ends of the helically wound ribbon by leads 23, 24. An'insulator plug 25 is mounted in the outer wall of the casing and comprises .a tubular section 26 and flanges 27 and 28 which cooperate with the outer wall of the casing to provide a moistureproof seal. A small choke coil 29 is positioned within the insulator plug and the tap 22 from the random coil 20 is connected to the choke coil' 29. The other end of the choke coil is provided with a tap for connection to the lead cable of a car radio. According to customary practice the exterior covering 30 of the lead cable is connected, to ground. A protective rubber boot 31 is mounted on the end of the cable and slidable into overlying relationship With the end of the insulator plug 25.

A second plug 32 is positioned in the outer wall of the casing at a point generally diametrically opposed from the first insulator plug and comprises flanges 33 and 34 which cooperate with the outer wall of the casing to form a moistureproof seal. The plug 32 is provided with an opening in which is positioned a pin 35 which projects outwardly from the plug and has the end thereof split .as at 36 to receive a wire 37. The wire 37 is preferably bent along its length to form an angle of approximately 120' (Fig. 1). A tap 38 is connected to the toroid coil 19 of helically wound ribbon near the end thereof opposite the end in which the ferrite piece is positioned and also to the pin 35, as shown in Figs. 2 and 3.

The plugs 25 and 32 are preferably made of polyethylene or synthetic rubber. An insulating covering 39 is provided around the helically wound ribbon and the random wound coil and insulates the ribbon and coil from the case. This coating preferably comprises a thermo-plastic material, such as wax, which may be applied by dipping.

The antenna may be mounted beneath an automobile 'by a suitable bracket 12 which electrically insulates the also preferably includes a flexible connection whereby in the event the antenna strikes a fixed object it will swing or pivot or pass over the object without breaking the antenna or the mounting bracket.

As shown in Fig. 6, a bracket for mounting the antenna may comprise a pair of arms 40 projecting downwardly from a metal plate 41 which is mounted on the bottom of the car and electrically insulated therefrom by an insulating member 42 of polyethylene, rubber or the like. The antenna is in turn mounted on the end of the arms by flexible members 43 such as pieces of rubber which permit relative movement between the antenna and the bracket. The provision of the flexible members 43 permits the antenna to move relative to the automobile in the event that it strikes an obstruction such as a rock and thereby prevents damage to the antenna or the bracket.

As shown in Fig. 7 the toroid coil 19 of helically wound ribbon is connected in series with the random wound coil 20. Tap 22 is connected intermediate the ends of the random wound coil 20 to the choke coil 29 which in turn is connected to the car radio through the cable. Static wire 37 is connected to the toroid coil 19 of helically wound ribbon near the end thereof opposite to that in which the ferrite piece is positioned.

A specific example of a satisfactory antenna comprises the following materials in the dimensions set forth below:

Casing:

Aluminum 8" average diameter. Toroid coil of helically wound ribbon:

29 turns, A" brass, .0040 thickness, A spacing between adjacent windings, /2 between the ends of the coil.

Core:

Flexible vinyl plastic, 4" width, height, 18"

length.

Ferrite piece: 7

A width, 1 height, 4%," length. Random wound coil:

Single strand magnetic wire coated .0159 diameter, random wound in form of D, turns, center tapped, and 3% more turns.

4 Choke coil:

Single strand magnetic wire coated .0159 diameter,

30 turns, A1" diameter with single turn spacing. Static wire:

Rod or wire 9 /2" in length bent to form 120 angle, connected to helically wound ribbon, 4 turns from the end of the ribbon opposite the end into which the ferrite piece is positioned.

An antenna embodying the invention has been found to be omnidirectional when mounted beneath a car with the casing lying in a generally horizontal plane. The sensitivity of the antenna is good and ignition interference is completely eliminated even in severe cases caused by excessive spark plug gap and the like.

The over-all capacitance of the antenna including a six foot lead is approximately 65 micromicrofarads, which is substantially less than the maximum micromicrofarads permissible by the trimming device in present-day automobile radios.

When tested, the above antenna was found to resonate at a frequency of 1345 kilocycles and to peak in a rather bro-ad, fiat top curve. The Q of the antenna with six foot lead ranges between 650 and 1260 at a frequency of 1000 kilocycles dependent on the type of mounting bracket used.

I have found that the minimum distance between the ends of the toroid coil of helically wound ribbon is five and a half inches. When the distance is made less than five and a half inches, the sensitivity of the antenna diminishes rapidly. I have also found that in order to obtain satisfactory results the tap which divides the random wound coil into two coils must be at such a point that the resultant coils are unequal in length. Although I do not wish to be limited by the theory, it is believed that dividing the random wound coil in this manner provides a coil of lesser windings for eliminating high frequency ignition interference and a coil of more windings for eliminating low frequency ignition interference.

I have also found that when the rod or wire 37 which projects outwardly from the housing is nine and a half inches or more, it not only provides a static discharge point but, in addition, increases the sensitivity by its electrostatic pick-up. When the wire is less than nine and a half inches in length, the static discharge properties are retained but the sensitivity properties are diminished or lost. When the wire is greater than nine and a half inches in length, no substantial increase in sensitivity properties has been observed. When a wire is used, it is preferably bent upwardly at a point intermediate its ends to permit its being flexed in the event that it strikes an obstruction, thereby preventing damage thereto.

I have further found that the height of the toroid coil 19 of helically wound ribbon should be greater than one inch. The diametrical distance between windings must be at least one quarter inch.

An antenna made in accordance with the invention has very low impedance and practically no resistance, the resistance being on the order of one-half ohm.

The various parts of the antenna are assembled in the following manner: The metal ribbon is first wound about the plastic core 19' and the ferrite piece 21. The random wound coil 20 is then wound and the tap 22 is made at the appropriate points intermediate the ends of the coil. The electrical connections 23, 24 between the toroid coil 19 and the random wound coil 20 are made and the entire unit is dipped into a bath of thermoplastic material such as wax and the coating is permitted to dry. During the assembly of the ribbon and the random wound coil, tape or other means may be used to prevent the unwinding thereof. After the thermoplastic coating is permitted to set, the electrical connections are made to the tap 38 and tap 22 and the entire unit is inserted in onehalf 16 of the metal casing 14 with the plugs 25,

32 in proper position. The other half 15 of the metal casing is then brought into position and the edges crimped or curled to seal the casing as at 17, 18. The entire casing with the coils therein is then dipped in a suitable protective coating composition, or the coating C may be applied by spraying to protect the casing from corrosion, moisture or abrasion.

A modification is shown in Fig. 8 wherein the housing is made of plastic material and comprises identical halves 50 which join together face to face to form a complete annulus. Ribs or walls 51 provide opposed grooves for locating the toroid coil 52.

The toroid coil 52 comprises a helically wound ribbon wrapped arounda core 53. The antenna includes an annular cardboard core, 5.5v about which a pair of low capacitance coils 56, .7. are Wound. One end of the coil 56 is connected to the toroid coil 52 by a short jumper 58. The other end of the coil 56 is joined to the other end of the toroid coil 52 by a jumper 59. This same end of the toroid coil 52 is also joined to one end of the coil 57 by a jumper 60. The other end of the coil 57 is connected at 61 to the lead 62 of the cable leading to the radio. The housings are joined together in sealed relation after the connections are made and at the same time a static elimination rod 63 is inserted at 64 in contact with toroid coil 52. The cable is supported in a metal sleeve 65 which is grounded to the frame of the vehicle in which the device is installed.

A supporting hanger bracket 66 has the free ends passing through a portion of the two halves 50 of the housing, joining them, and mechanically locking the two halves together and, in addition, providing means for attaching the device to the vehicle frame.

The circuit embodied in the form of the invention shown in Fig. 8 is such that the toroid coil 52 is in series with the coil 56, while the coil 57 is in series with the lead 62 of the cable.

However, the preferred wiring diagram would comprise the circuit shown in Fig. 7. The antenna shown in Fig. 8 would have the various coils thereof connected in the following manner in order to provide the circuit shown in Fig. 7: The toroid coil 52 and the coils 56, 57 would be connected in series and a lead would extend from a point between the coils 56, 57 to the lead in the cable extending to the radio. The static rod 63 would be electrically connected to a point along the length of the toroid coil 52 as shown in Fig. 8.

It can thus be seen that I have provided an antenna which may be positioned below a vehicle such as an automobile and which satisfactorily fulfills basic requirements which are essential in a radio antenna. The antenna is omnidirectional and has good sensitivity over the entire range of radio frequency. The antenna is capable of discriminating against ignition interference, resonates at an intermediate frequency between the ends of the broadcast bands and has a flat curve of sensitivity. The capacitance of the antenna and a lead is sufficiently low as to permit compensation by the trimmer of present-day automobile radios.

This application is a continuation-in-part of my copending application entitled Radio Antenna, Serial No. 378,261, filed September 3, 1953.

I claim:

1. A radio antenna for vehicles such as automobiles and the like comprising a hollow casing, a toroid coil of helically wound ribbon mounted in said casing, said toroid coil ribbon having the ends thereof spaced apart, a ferrite piece positioned in and connected to one end of said helically wound ribbon, a pair of coils electrically connected in series with said helically wound ribbon, said coils being random wound and comprising a plurality of juxtaposed loops of wire positioned adjacent said toroid coil, a tap connected between said coils and projecting through said casing, and a second tap connected near the end of said toroid coil opposite the end 6 in which the ferrite piece is positioned and projecting through the casing, said coils and taps being electrically insulated from said casing.

2. The radio antenna set forth in claim 1 wherein said ends of the toroid coil of helically wound ribbon are spaced apart a distance of at least five and a half inches.

3. The radio antenna set forth in claim. 1 wherein said helically wound ribbon of the toroid coil is at least onequarter inch in width and adjacent convolutions of said coil are not less than one-quarter inch apart.

4. The radio antenna set forth in claim 1 wherein a choke coil is provided in series in the tap connected between said pair of random wound coils.

5. The radio antenna set forth in claim 1 wherein said pair of random wound coils is positioned below said toroidal coil.

6. The radio antenna set forth in claim 1 wherein said toroid coil and said randomwound coils are electrically insulated from said casing by a layer of thermoplastic insulating material.

7. The radio antenna set forth in claim 1 wherein said hollow casing comprises an annular hollow D-shaped ring.

8. The radio antenna set forth in claim 7 wherein said portion of the toroid coil with the ferrite piece therein is positioned in the straight portion of the D-shaped housing.

9. The radio antenna set forth in claim 1 wherein said hollow casing is made of metal, and a coating of protective material is provided on the outer surfaces of said casing.

10. An antenna for receiving radio frequency waves and adapted to be used on vehicles such as automobiles and the like comprising a low impedance first winding of helically wound conductive ribbon disposed about a circular axis, a core of ferrite iron disposed through a portion of said first winding, a second winding composed of a pair of coils, said first Winding and said second winding being connected in series in a closed circuit, and a lead Wire connected to said second winding.

11. The antenna set forth in claim 10 including a static wire connected to said first winding and projecting radially outwardly.

12. The antenna set forth in claim 10 including a hollow casing in which said windings are positioned, said lead wire projecting through said casing.

13. The radio antenna set forth in claim 11 wherein said static wire is connected to said first winding at a point near the end thereof.

14. The radio antenna set' forth in claim 10 in combination with a vehicle, and means for supporting said antenna on said vehicle.

15. The radio antenna set forth in claim 10 wherein said pair of coils comprising said second winding are unequal in length.

16. An antenna circuit comprising a coil of helically wound ribbon, a pair of coils connected in series in a closed circuit with said ribbon coil, and a lead connected between and extending from said pair of coils.

17. The circuit set forth in claim 16 wherein a choke coil is connected in series with said lead.

18. The circuit set forth in claim 16 wherein a static discharge wire is connected to said ribbon coil intermediate its ends.

19. A radio antenna for vehicles such as automobiles and the like comprising a casing forming an annular chamber, a toroid coil positioned in said annular chamber, said toroid coil comprising a ribbon helically wound about a core and a ferrite piece, the ends of said toroid coil being spaced apart, a random wound coil positioned in said annular chamber and electrically connected in series with said toroid coil, said random wound coil comprising a plurality of juxtaposed loops of Wire, said random wound coil including a center tap separating said coil into a pair of coils, said tap projecting through said casing and adapted to be electrically connected to the cable leading to a radio, and a second tap connected near the end of said toroid coil opposite the end in which the ferrite piece is positioned and projecting through the casing, said second tap being adapted to be electrically connected to a static Wire.

20. The radio antenna set forth in claim 19 wherein said casing comprises a pair of complementary annular metal members, said members being generally U-shaped in cross section and adapted to be brought into engagement to form an annular chamber, and means insulating said taps which project through said casing from said metal members which comprise the casing.

21. The radio antenna set forth in claim 20 wherein said means insulating said taps comprises a plug surrounding each said tap and adapted to provide a moisture seal with said casing.

22. The radio antenna set forth in claim 21 wherein a choke coil is positioned within said plug surrounding said tap.

23. The radio antenna set forth in claim 21 wherein said plugs are made of polyethylene.

24. The radio antenna set forth in claim 19 including a static wire, saidstatic wire being at least nine and one half inches in length.

References Cited in the file of this patent UNITEDSTATES PATENTS 1,792,964 Brooks et a1. Feb. 17, 1931 1,875,358 Sola Sept. 6, 1932 2,055,830 Vincent Sept. 29, 1936 2,383,286 Beers Aug. 21, 1945 FOREIGN PATENTS 9233/27 Australia May 10, 1928 430,548 Great Britain June 20, 1935 1,008,359 France Feb. 20, 1952 

